In the field of microscopes used for scanning biological samples and the like, it is often necessary to refocus the objective lens rapidly in order to compensate for variations in thickness of the biological sample being inspected. This is done by moving the microscope objective lens relative to a support member so as to adjust the distance between the objective lens and the sample. It is difficult to move an objective lens rapidly because the lens and its support assembly typically weigh over 100 grams but in the past this has been achieved by mounting the objective lens support assembly to a piezoelectric element and applying a suitable control signal to the element to cause the element to move the support assembly. The problem with this known arrangement is that a piezoelectric element can only move the microscope objective lens and its support assembly by relatively small amounts, typically less than 500 microns and at relatively low accelerations while requiring purpose built actuators.